1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery apparatus such as a lithium ion battery and a method for charging an anode of the apparatus.
2. Background Art
Nonaqueous electrolyte secondary batteries typified by lithium ion batteries have high energy densities and are thus gathering much attention as batteries for electric cars. Target electric cars include zero-emission electric cars with no engine mounted therein, hybrid electric cars with both an engine and a secondary battery mounted therein, and plugin electric cars charged directly by a system power source. Furthermore, the nonaqueous electrolyte secondary battery is expected to be used as a stationary power storage apparatus in which power is stored so that power is supplied in an emergency when a power system is shut off.
For such diverse applications, high durability is demanded of the lithium ion battery. That is, the lithium ion battery is desired to undergo only a small decrease in chargeable capacity in spite of an elevated environmental temperature and to maintain a high battery capacity retention ratio over a long period. In particular, the lithium ion battery for electric cars suffers a high temperature environment at 60° C. or higher resulting from radiation heat from a road surface or heat conduction in the car. Thus, the preservation property and cycle life in such a high temperature environment are important required performance for the lithium ion battery for electric cars.
In order to suppress a decrease in capacity or cycle degradation when the battery is left at high temperature, various techniques for obtaining durable electrode materials or electrolytic solutions have been studied. Furthermore, techniques have also been studied in which lithium is inserted into an anode to eliminate the cause of a decrease in capacity. JP Patent Publication (Kokai) No. 10-270090A (1998), JP Patent Publication (Kokai) No. 11-31531A (1999), and JP Patent Publication (Kokai) No. 7-254435A (1995) describe examples in which lithium is inserted into the anode.